1. Field of the Invention
The present invention relates generally to water purification systems, primarily of the reverse osmosis type and more specifically to a flow restrictor for use therein and especially for installation between the waste water output of a reverse osmosis membrane canister and the drain to which the water purification system is connected, primarily for providing a selected hydraulic impedance for dropping the pressure from the feed water pressure level to the drain water pressure level.
2. Prior Art
The use of a flow restrictor in a reverse osmosis water purification system is well known. Flow restrictors for reverse osmosis systems come in a variety of configurations including orifice types, ball and seat types, needle valves and capillary types. Water pressure within the reverse osmosis system is at the feed water pressure level which is usually between 40 psig and 100 psig. However, because a relatively small percentage of the water passing through a reverse osmosis system is actually converted to purified water, a significant portion of the input water must be output to the drain to which the water purification system is connected. Because the typical drain pressure is at 0 psig, the principal purpose of the flow restrictor is to provide the required hydraulic impedance to permit an orderly reduction in the pressure level between the feed water pressure level and the drain pressure level and thus limit flow therebetween. Capillary type restrictors are inherently superior to orifice type restrictors because they are less likely to become clogged. In the past, such capillary flow restrictors have been relatively expensive and difficult to configure and manufacture. One reason for this expense and difficulty is the fact that pressure reduction is usually accomplished by passing the waste water through a relatively long, narrow teflon tube. Teflon is the usual material of choice for this tube because it resists the inadvertent and undesirable accumulation of mineral and sedimentary constituents of common feed water supplies as well as bio-foulants therein. Such an accumulation could inadvertently clog the flow restrictor tube which could then block the release of waste water and create havoc in the form of damage to the reverse osmosis membrane. Thus, teflon is selected because of its extremely low friction characteristics and also because it is an extremely inert material which does not readily adhere to any of the extraneous material in feed water and does not chemically degrade. Unfortunately, because of its low friction characteristics and its resistance to any form of adhering, teflon tubing is a difficult material to stabilize mechanically within a flow restrictor housing. Without such mechanical stabilizing, the teflon tube can be readily displaced from its desired position by the water pressure through the tube and ultimately produce leaks or otherwise create faults which can wreak as much havoc as a blocked tube. Two exemplary prior art teflon tube flow restrictors will be described hereinafter in more detail and it will be seen that there is still an ongoing need for a flow restrictor of the type which uses an elongated, narrow passage teflon tube which overcomes the mechanical stabilizing difficulties of the prior art, while also providing a means for reducing the mechanical complexities and commensurate expense of manufacturing such flow restrictors.